1. Field of the Invention
The present invention generally relates to wireless communications, and more particularly to estimating power in a wireless mobile communication system.
2. Description of the Related Art
A multiple access method performs wireless communications by allowing a plurality of users to share time and frequency simultaneously. Multiple access methods include frequency division multiple access (FDMA) methods, time division multiple access (IDMA) methods, and code division multiple access (CDMA) methods. The FDMA method allocates one frequency per user.
The TDMA method is performed by adding a time division notion to a frequency division notion of the FDMA method. Also, in TDMA, a voice signal is converted into a digital frame or packet to be transmitted, and each channel is divided into a short time period.
The CDMA method is a spread-spectrum technique, in which a plurality of users simultaneously share time and frequency. Each user is allocated a specific code, and a transmitter and receiver have to be synchronized in order to modulate and demodulate code spread data.
Generally, functions performed in TDMA/CDMA methods are certified by estimating a quality of output power of a base station or mobile station. Time domain power is estimated in the TDMA method and a code domain power is estimated in the CDMA method, and equipment for estimating time domain power is different from equipment for estimating code domain power. Therefore, conventionally, equipment for estimating the time domain power can only be used in a TDMA system, and equipment for estimating code domain power can only be used in a CDMA system.
In order to measure the quality of output power, in a CDMA method a certain allocated frequency band is divided into different codes to distinguish respective channels. At this time, transmission frequency and receiving frequency are different from one another. A duplexer may therefore be used at a high frequency end. In contrast, in a TDMA method, the same frequency band is allocated for transmitting and receiving data, and transmission and reception channels are distinguished by time division switching. A time division switch is used at the high frequency end during this technique.
Certifying a function of a mobile communication system by estimating the quality of output power of a base or mobile stations is important. This process is widely used over the entire mobile communication industry, for example, to perform quality testing during the manufacture of a mobile station, to measure communication quality between base and mobile stations, and to operate one or more radio resources.
FIG. 1 is a graph showing a time domain power measurement in a global system for mobile communication (GSM) method employing TDMA. In the graph, a frequency band allocated to an up-link and a down-link in the GSM method is divided into each channel, and the divided channel is again divided into time slots using a TDMA method. That is, the channel is divided into time slots (or burst periods), the most basic unit in TDMA.
The up-link denotes a transmission path from a mobile station to a base station, and the down-link denotes a transmission path from a base station to a mobile station. One TDMA frame is divided into 8 time slots (TS0-TS7), and power is estimated for each time slot based on this arrangement. Power is represented by dBm units. Time slot TS0 is allocated to the down-link and is used to transmit a data signal or operational information from a base station for controlling a mobile station. The remaining time slots TS1-TS7 are allocated to the up-link and down-link, and are used to detect and display levels operated on each channel.
FIG. 2 is a graph showing a code domain power measurement performed in an IS-95 method. In this method, 64 (0-63) channels are used and each channel has an output power which is estimated and displayed in the graph. The code domain power is represented in dB units. In estimating and displaying the code domain power based on a CDMA method, the signal power of each channel and noise power is simultaneously estimated. In FIG. 2, channels 3, 6 and 59 are shown as having power which is greatly decreased compared to the power of the remaining channels, which, for example, have not received data to be transmitted. The measurement results are displayed together on one screen, so that a signal-to-noise ratio (SNR or S/N) can be easily recognized.
In order to distinguish channels in the CDMA method, a Walsh code is generally used. Because multiple users use the same frequency in a CDMA method, power management is necessary. Accordingly, base station power is estimated by being distinguished based on Walsh codes, and a code domain power is estimated by comparing a non-operational code power with a total power, thereby properly distributing power. This also reduces interference between channels and maximizes capacity of a section.
FIG. 3 is a chart showing a state of a channel allocated by a Walsh code length in a general CDMA method. When the Walsh code length is 4 (L=4), 4 channels 0-3 are allocated. When the Walsh code length is 8 (L=8), 8 channels 0-7 are allocated. And, when the Walsh code length is 16 (L=16), 16 channels 0-15 are allocated. From these chart entries, it can be seen that channel allocation is proportional to the Walsh code length, L.
As previously mentioned, in order to estimate transmitting power in a CDMA system, code domain power estimation for estimating an output power per channel is performed. However, because transmitting frequencies of the base station and mobile station are different, and because the TDMA method was not introduced for each CDMA channel, no method for estimating the code domain power in a TDMA method has heretofore been proposed. Moreover, a method for estimating the time domain power in a CDMA method has not been proposed.
Therefore, there is a problem in that a method for performing power estimation in a code region in next-generation mobile communication systems where TDMA and CDMA methods are mixed, such as but not limited to wideband CDMA time division duplex (WCDMA TDD) systems and time division synchronous CDMA (TD-SCDMA) systems.